Engineering topics

Chung, Sheng-Heng

Publications and source records attributed to Chung, Sheng-Heng.

4 records

DOE OSTI2018

An ant-nest-like cathode substrate for lithium-sulfur batteries with practical cell fabrication parameters

We report that electrochemical performances of lithium-sulfur batteries have received much progress in recent years. However, their practical deployment encounters challenges with respect to optimizing the cell-fabrication parameters (e.g., amounts of the active material and electrolyte). We present here an “ant-nest-like” cathode substrate with unique architecture to synchronously attain high electrochemical performance and necessary cell-fabrication parameters. The cells with a high sulfur loading (11.5 mg cm -2 ), a high sulfur content (75 wt.%), and a low electrolyte/sulfur ratio (9 μL mg -1 ) display a high areal capacity and energy density of, respectively, 7 mA h cm -2 and 14 mW h cm -2 with a capacity retention of 70% after 150 cycles. Moreover, the cells exhibit a low self-discharge behavior with a low self-discharge constant of 0.0013 per day and a long rest period of one month. Lastly, these dynamic and static electrochemical stabilities are attributed to the ant-nest-like structure and low surface area of the cathode substrate that allows, respectively, the accommodation and encapsulation of a high amount of active material and reduces the consumption of electrolyte.

25 ENERGY STORAGE↗

DOE OSTI2018

A core–shell cathode substrate for developing high-loading, high-performance lithium–sulfur batteries

Lithium–sulfur batteries with a high theoretical energy density would be a promising next-generation energy-storage system if their cell-fabrication parameters (e.g., sulfur loading/content and the electrolyte/sulfur ratio) are improved to a practically necessary level. In this article, we report the design of a three-dimensional core–shell carbon substrate, integrating a porous internal core with a conductive external carbon nanofiber shell. Such a carbon substrate encapsulates a high amount of sulfur as the active material core to form a high-loading core–shell cathode, attaining an ultra-high sulfur loading and content of, respectively, 23 mg cm -2 and 75 wt%. With distinguishable internal and external regions, the carbon substrate facilitates the redox reactions and hinders the polysulfide diffusion. Therefore, the core–shell cathodes exhibit a high areal capacity and energy density of, respectively, 14 mA h cm -2 and 27 mW h cm -2 during cycling. During resting, they achieve a long shelf-life of one month with a low capacity-fade rate of 0.25% per day.

25 ENERGY STORAGE↗

DOE OSTI2018

Progress on the Critical Parameters for Lithium-Sulfur Batteries to be Practically Viable

Lithium–sulfur batteries have great potential to satisfy the increasing demand of energy storage systems for portable devices, electric vehicles, and grid storage because of their extremely high specific capacity, cost-effectiveness, and environmental friendliness. In spite of all these merits, the practical utilization of lithium–sulfur batteries is impeded by commonly known challenges, such as low sulfur utilization (<80%), short life (<200 cycles), fast capacity fade, and severe self-discharge effect, which mainly result from the i) low conductivity of the active material, ii) serious polysulfide shuttling, iii) large volume changes, and iv) lithium–metal anode contamination/corrosion. Numerous approaches are reported to effectively mitigate these issues. Indeed, such approaches have shown enhanced lithium–sulfur battery performances. However, many reports overlook the critical parameters, including sulfur loading (<13 mg cm-2), sulfur content (<70 wt%), and electrolyte/sulfur ratio (>11 µL mg-1), that significantly affect the analyzed electrochemical characteristics, energy density, and practicality of lithium–sulfur batteries. This review highlights the trends and progress in making cells fulfilling these fabrication parameters and discuss the challenges of the amount of sulfur and electrolyte in fabricating cells with practically necessary parameters and with high electrochemical utilization and efficiency.

25 ENERGY STORAGE↗

DOE OSTI2018

Three-Dimensional Graphene–Carbon Nanotube–Ni Hierarchical Architecture as a Polysulfide Trap for Lithium–Sulfur Batteries

We report that despite their high energy density and affordable cost compared to lithium-ion (Li-ion) batteries, lithium-sulfur (Li-S) batteries still endure from slow reaction kinetics and capacity loss induced by the insulating sulfur and severe polysulfide diffusion. To address these issues, we report here nickel nanoparticles filled in vertically grown carbon nanotubes on graphene sheets (graphene-carbon nanotube-nickel composite (Gr-CNT-Ni)) that are coated onto a polypropylene separator as a polysulfide trap for the construction of high-loading sulfur cathodes. The hierarchical porous framework of Gr-CNT physically entraps and immobilizes the active material sulfur, while the strong chemical interaction with Ni nanoparticles in Gr-CNT-Ni inhibits polysulfide diffusion. The covalently interconnected electron conduction channels and carbon shell-confined metal active sites provide feasible paths for the continual regeneration of active material during the charge/discharge process. Benefitting from these novel morphological and structural features, the Li-S cell with the Gr-CNT-Ni as a polysulfide trap demonstrates high specific capacity and good cycle life. Lastly, this work provides new avenues for synergistically combining the advantages of hierarchical porous carbon architectures and metal active sites for the development of high-performance cathodes for Li-S batteries.

25 ENERGY STORAGE↗